Okay, it turned out my site still had its development URL being used by Jetpack Protect behind the scenes (even though Jetpack debug showed things as okay and the site otherwise using the live URL for years now [might be good to have Jetpack debug also check if Jetpack Protect is using the same URL as the main connection & return results accordingly.])
Once Jetpack support addressed this issue (thanks, Megan & Ryan!), per it not being surfaced anywhere for me that I know of, they also confirmed the proxy setup was already good-to-go with no changes needed there.
I still saw Cloudflare IPs when viewing the IP Jetpack’s settings show in the Protect settings. I then cleared my server-side cache and Cloudflare cache (I use W3 Total Cache with the Cloudflare extension so this just took 1 click to clear all caches.) Finally, the site was showing the correct visitor IP!
In summary, I just needed to contact Jetpack support to tell me there was an issue with a URL within their system which they then fixed, I cleared all caches on the site & Cloudflare’s end, and then I confirmed things were working properly after that. The big takeaway is that Jetpack support can really be vital (with Jetpack unfortunately sometimes having settings be misconfigured that then aren’t surfaced outside of Jetpack’s own internal systems, currently.)